Entities are used to define shortcuts to special characters.
Entities can be declared internal or external.
<!ENTITY entity-name "entity-value">
DTD Example:
<!ENTITY writer "Donald Duck.">
<!ENTITY copyright "Copyright W3Schools.">
XML example:
<author>&writer;©right;</author>
注: An entity has three parts: an ampersand (&), an entity name, and a semicolon (;).
<!ENTITY entity-name SYSTEM "URI/URL">
DTD Example:
<!ENTITY writer SYSTEM "https://www.w3schools.com/entities.dtd">
<!ENTITY copyright SYSTEM "https://www.w3schools.com/entities.dtd">
XML example:
<author>&writer;©right;</author>